Migrant workers are believed to act as a bridge population in the spread of HIV. However, migration patterns are highly variable, influenced by local historical and socio-economic contexts. In India, rural-to-urban, circular migrant workers are a priority group for HIV interventions. Their success requires an understanding of the processes influencing migrant vulnerability and how the migration-HIV relationship evolves over time. I conducted a systematic review examining the association between migration and HIV prevalence. I also analysed behavioural survey data from a study on migrant men to quantify and characterise those at greatest risk. For the case study, I carried out qualitative fieldwork in Allahabad district, an area of high rural-to-urban, circular migration and increasing HIV prevalence. I conducted interviews in two settings: clinical and rural village. I interviewed HIV-positive individuals at an HIV-treatment centre and migrant men and wives of migrants in two high out-migration villages. Published studies showed some association between circular migration and HIV, but migration was defined inconsistently across publications. According to survey data 20% of migrant men had non-spousal sexual partners at multiple locations; this was associated with self-perception of HIV risk, age and recent migrant status. The qualitative case study showed specific factors such as nature of social group and migration location affecting risk of infection. Following infection, migrant status delayed contact with HIV services, depleting household savings on private treatment for HIV-related conditions and facilitating onward transmission. After enrolment with HIV services, diminished health, a rigid ART regime and job insecurity hindered resumption of migration-based livelihoods. Increased HIV risk in migrants is due to the context of migration not mobility itself. Despite free testing and treatment services, migrant workers and their families are being diagnosed late. The risk to migrant livelihoods from HIV has strong implications for long-term ART adherence and prognoses.